Plasticizing agents for nitrocellulose



Jan. 15, 1963 J. COHEN ETAL PLASTICIZING AGENTS FOR NITROCELLULOSE Filed March 29, 1956 2 Sheets-Sheet 1 OR EX, 3 1

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PRESSURE (PSI) INVENTORS RONALD A. HENRY WILLIAM G FINNEGAN JOSEPH COHEN (\T. W ATTORNEYS OOOn 2 Sheets-Sheet 2 Exes L/ zxzz PRESSURE (PSI) RONALD A HENRY OOON I INVENTORS WILLIAM G. FINNEGAN JOSEPH COHEN /P 08w 0 v 83 coo. m 4 0cm.

J- COHEN ETAL PRESSURE (P PLASTICIZING AGENTS FOIR NITROCELLULOSE Filed March 29, 1956 Jan. 15, 1963 h oow X /./I /D E 32 com l) /L 6 /e o 08 a 5 2. 5 a y 7 O o I 5 53.5 NEE wzEmnm lz o8 a E 2 o l o E O 9 8 7 6 w 4" 5 2 5 W I. O Q 0 Q 0 0 0 2 O ATT'oRNEYs PLASTICTZING AGENTS FOR NITRGCELLULOSE Joseph Cohen, Arcadia, and William G. Finnegan and Ronald A. Henry, China Lake, alif., assignors to the United States of America as represented by the Secretary of the Navy Filed Mar. 29, 1956, Ser. No. 574,939 11 Claims. {CL 14992) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to improved propellent compositions for jet actuated devices, more particularly, it relates to propellent compositions incorporating improved plasticizers.

In the art of compounding propellent compositions for jet actuated devices it is well known that plasticizers are essential to the compositions for providing the required plasticity to permit homogeneous mixing of the raw materials and to provide a finished propellent grain which is well plasticized and not subject to cracking or breaking. A suitable plasticizer, in addition to being capable of imparting plasticity to the propellent composition and to the finished propellent grain, must possess a number of other well defined properties. Its presence in the composition should not undesirably affect the highly sensitive ballistic properties of the propellant, such as, the mesa and plateau effect of propellants for jet actuated devices. Further, incorporation of the plasticizer in the propellent composition should not undesirably affect the surveillance characteristics and thermochemical properties of the composition. Additionally, the plasticizing agent should preferably have a high nitrogen content, thus assuring a low average molecular weight for the combustion products.

Representative plasticizers ordinarily incorporated in double base propellent powders are dialkyl phthalates such as dimethyl and diethyl phthalate, ethyl centralite, dibutyl sebacate and nitroglycerin, the latter being an explosive plasticizer. None of these plasticizers, with the exception of ethyl centralite, function to remove certain oxides of nitrogen generated in propellants during storage which shorten the storage life of the propellants. Further, of the named compounds only nitroglycerin contains an appreciable percentage of nitrogen.

It is, therefore, an object of this invention to provide propellent compositions for jet actuated devices possessing a high degree of plasticization.

It is another object of this invention to provide highly plasticized propellent compositions for jet actuated devices which have good ballistic and thermochemical properties as well as good surveillance properties.

It is still another object of this invention to provide homogeneous propellent formulations in which the plasticizer, in addition to its plasticizing effect, also functions as a coolant by providing a large percentage of nitrogen.

It is a further object of this invention to provide propellent compositions for jet actuated devices which produce combustion products having a low average molecular weight.

It has been found that the above and other objects are accomplished by homogeneously incorporating derivatives of tetrazole into propellent compositions in amounts varying from about percent to about 50 percent, depending upon the particular derivative and the compositions into which it is incorporated.

The derivatives of tetrazole disclosed herein as plasticizers have a high nitrogen content, generally over 30 percent, the parent compound itself having a nitrogen ice content of percent. This is contrasted with the 10.4 percent of nitrogen in ethyl centralite and 18.5 percent of nitrogen in nitroglycerin. Further some of these derivatives have the property of absorbing oxides of nitrogen released from propellants on standing. An advantage of the derivatives of tetrazole over prior non-explosive plasticizers for propellent compositions for jet actuated devices is the superior degree of gelation or colloiding of nitrocellulose produced by them. When they are mixed with nitrocellulose they produce a gel of varying degree, dependent upon the particular derivative which is used and on the relative percentages of the derivative and the nitrocellulose. When a complete propellent composition is processed to contain nitrocellulose, the tetrazole derivative, nitroglycerin, and the various other conventional additives to propellants for jet actuated devices, such as ballistic modifiers, stabilizers, and others, the colloiding effect on the nitrocellulose is so effective that a uniformly distributed matrix incorporating the other ingredients of the composition is formed. Furthermore, the absorption by nitrocellulose of other ingredients of the composition which are ordinarily physically compatible with nitrocellulose, is not inhibited by the presence of the tetrazole derivatives. Illustrative of the superior plasticizing effect of the tetrazole derivatives is the fact that, whereas it is common practice to include approximately equal weights of nitrocellulose and total plasticizer in double base propellent compositions it has been found that the ratio of nitrocellulose to the total amount of plasticizer, when one of the tetrazole derivatives is included, can be as high as 2 to 1 and still give a properly colloided composition. This is illustrated by a comparison of the plasticizing effects produced in a conventional propellent composition by a standard plasticizer, ethyl centralite, and by a representative member of the tretrazole derivatives, 1-ethyl-S-ethylaminotetrazole, the compositions being as follows:

Despite the substantially larger ratio of total plasticizer to nitrocellulose in the composition of Example I, strands produced from the composition of Example 11 were found to be less brittle and more flexible than those produced from the composition of Example I.

The invention is best understood by reference to the description which follows, taken in connection with the drawings, which form a part of this specification and in which the FIGS. 1-4, inclusive, are graphs of the pressureburning rate relationship of propellent compositions of the invention.

Table I below contains 24 examples of propellent compositions of the invention which were selected as representative from among those prepared and tested. The examples include a sampling of compositions containing 13 representative tetrazoles as plasticizers, some tetrazoles being used in more than one composition. Examples 1-7, inclusive, 9-13, inclusive, and 15-20, inclusive, and 24 are examples of propellants made by incorporating the tetrazole plasticizers in conventional double base propellants, the propellent composition being set forth in the table. Examples 22, 23, 25, 26 and 27 are of propellent compositions made by incorporating tetrazole plasticizers which were made for comparative purposes. Example 21 is a blank of a conventional cool gun propellent composition, cordite-N. All of the formulations were made by the solvent process, a conventional manufacturing method used for double base and cool gun propellants. Other processes may be used, the only requirement being that a'process be used which insures that the plasticizer is uniformly and homogeneously incorporated throughout the propellant in its finished state. This can only be insured by a thorough mixing and incorporating of the plasticizer in'the form of small particles in the raw propropellant mix, such as'is done in the solvent or solventless process mentioned above.

The following compounds were tested as plasticizers with nitrocellulose and found to be compatible and excellent plasticizers at the percentage level indicated.

TABLE I [Weight percent] Example .123 4 5 67 8 9 1011 12 INGREDIENT 1 Passed through 200 on 270 mesh.

Key to Table I:

NCNitrocellulose (12.6%)

NGNitroglyc-e1in DEP-Diethy1 phthalate DBSDibuty; sebacate EC-Eethyl eentralite 2-NDPA-2-nitrodiphenylamine PbSalLead salicylate CW-Candeli1la Wax 1-B-5-BAT--1- hutyl-5-butylaminotetrazole.

5WIAT-5-methylaminotetrazole 5-EAT-5-ethy1aminotetrazole The tetrazole plasticizers were found to be compatible with the propellent compositions over wide percentage ranges. All of the compositions were well plasticized. Compatibility tests, heat stability and other surveilance tests, flex tests, temperature of explosion tests, second order transitions tests, burning rate tests, and other tests showed that the compositions were satisfactorily plasticized, that they had good surveilance characteristics, had no deleterious effects on required ballistic characteristics of propellants and even increased the burning rate of double base and cool gun propellentcompositions.

Typical results of tests performed on representative compositions shown in Table I are included in the following paragraphs.

Z-ethyltetrazole and 1,5-dimethyltetrazole were tested as plasticizers for nitrocellulose by the sorption method with the following results: The Weight of nitrocellulose in the presence of 2-ethyltetrazole was increased by 182% after 3 hours at. C., indicating that this tetrazole solvates nitrocellulose strongly. The weight of nitrocellulose in the presence of l,5-dimethyltetrazole was increased 45.5% after 75 minutes at 40 C. indicating satisfactory compatibility. 1-ethyl-5-ethylaminotetrazole was found to be compatible with cellulose acetate up to about the 30% level indicating the versatility of the tetrazoles as plasticizers.

-OAT5-octy1amin0tetrazole -DAI'5-decylaminotetrazole -5-AT1-methyl5-arninotetrazole -E-5-AT1-erhy1-5-an1inotetrazole E AEthyl (I-tetrazolyl acetate 2GNit roguanidine 1- 5-T -2-N1 t 5-tetrazolyl) -2-nitroguanidine G'Guanidinium Average Average Plasticizer film Number of thickness, folds to inches break None 0. 00175 3 .4 l-ethyl-Sethylaminotetrazole 0. 00177 380 l-methyl-5ethylaruinotetrazole 0. 00207 292 1-allyl-5-ally1arninotetrazole 0. 00196 454 l-methyl-5-methylaminotetra-zole 0. 00177 511 Comparison of the results obtained from the plasticized'. compositions With that obtained on the blank graphically illustrates the general effectiveness of the tetrazole plasticizers.

Second order transition temperatures for representative members from Table I are included below.

Example Results 7 No peak in the dielectric power loss curve occurred from 50 to 14 0. Films were tough and flexible. 16 Peaked at 8 0.

Peaked at 20 C. Peaked at 18 0.

temperature. No peak in dielectric power loss curve from 63 C. to The film was tough and flexible at room temperature. Peal-zed at -21 0. Films were tough and flexible.

The film was tough and flexible at room [Average time in seconds for explosion at temperatures shown] Example 298 330 372 397 412 428 458 485 510 C. C. C. C. C. O.

The extended time of explosion at the temperatures shown further indicates the stability of the compositions.

To supplement the heat stability tests given below for double base propellent formulations incorporating the plasticizers, heat stability test results obtained on Examples 22 and 25, cool gun propellent compositions, are included as follows: The compositions darkened in heat stability tests at 136 C. but did not explode during 8 hours. Oxides of nitrogen were not evolved, as indicated by the fact that the methyl violet paper used for indicating stability did not develop a pink or salmon color.

Graphs of representative results of standard burning rate tests performed on typical compositions of Table I are included as FIGS. 1, 2, 3 and 4. The graphs are logarithmic plots in which the burning rate of the propellant is plotted against pressure, the divisions on the abscissa representing multiples of 100. Inspection of the graphs shows that ballistic properties of the propellants are actually enhanced by incorporation of the plasticizers therein. For example, comparison of the graphs for the blanks 8 and 14 of FIG. 2 and the blank 21. of FIG.

4 with the graphs'for the other compositions shows that the burning rate is appreciably increased by the presence of the plasticizer. While some of this efiect for Examples 25, 26 and 27 of FIG. 4 must be attributed to the use of the new cool gun base compounds, it is quite 0bvious that some of the effect is due to the plasticizers.

Tables Ill and IV below present results of heat stability tests performed on propellent compositions containing varying amounts of tetrazole plasticizers. For

10 making the tests the weighed ingredients were dissolved in acetone by tumbling in sealed bottles for 24 hours and the resulting solutions cast into films on glass and dried for 2.5 days.

TABLE III 15 [The compositions consisted of 37% nitrocellulose (12.6%

N), 30% nitroglycerin, and 33% of the tetrazole derivative-tests performed at 136 (3.]

First salmon Definite Explosion Example Compound color on salmon or decomcolor, min. position min.

l-M-fi-DMAT 25 1 Melted but no explosion. 2 Melted after 10 minutes, frothed after 55 minutes. 3 Melted after 7 minutes. frothed after 20 minutes. Key to Table III excluding those terms used in Table I:

5-DMAT5-dimethylaminotetrazole 5-DAAT-5-diallylamin0tetrazole 5-HAT5-heptylaminotetrazole 5-PAT-5-phenylaminotetrazole 1-(m-CP)-5-AT-1-(rn-chlorophenyl) -5-aminotetrazole 2-E-5-AT2-ethyl-5-arninotetrazole 2-M-5-MAT-2-1netl1y15-methylaminotetrazole 2-M-5-NT2-methyl-5-nitrotetrazole 1-M-5-DMAT1-inethyl-5-dimethylaminotetrazole In order to illustrate the heat stability of different percentage compositions of propellants as well as the compatibility of the tetrazole plasticizers with a conventional stabilizer, Z-nitrodiphenylamine, the results of Table IV are included.

TABLE IV Example 45 46 47 48 49 Ingredient:

N C (12.6%) s N G 2-M-5-MAT Heat stability. 106 0.:

First salmon color on methyl violet paper,

minutes None 270 43 None 47 Definite salmon color,

minutes None 53 None Explosion or extensive decomposition, minutes. None None None None None Heat stability, 136 0.:

First salmon color, minutes 27 27-46 53 28 Definite salmon color,

minutes 35 71 44 Explosion or extensive decompositiomminutes. 64 None 12 None 40-49 None 107 110 None None None None None r 9. 5 58 None 28-33 7 43-68 52 properties than the homogeneous system formed by this invention. Further, the fact that this compound is hygroscopic seriously detracts from its value as a component of propellent formulations. As respects solvating and plasticizing power this compound is not the equivalent of the tetrazole plasticizers set forth above.

A number of the tetrazole derivatives and the cool gun propellants disclosed above arenew or relatively unknown, so that it is believed expedient to cite references to methods of preparation for those which have been' previously preparedand to give the method of preparation for those which are new. The method of preparation of the following compounds is given in Preparation and Isomerization of S-Alkylaminotetrazoles, by William G. Finnegan, Ronald A. Henry, and Eugene Lieber, published in volume 18, No. 7, of The Journal of Organic Chemistry, July 1953: S-methylaminotetrazole, S-dimethylaminotetrazole, S-ethylarninotetrazole, S-phenylaminotetrazole, 1-methyl-S-aminotetrazole, l-ethyl-S-aminotetrazole, 1-methyl-5-methylaminotetrazole, 1-methyl-5- dimethylaminotetrazole and 1-ethyl-S-ethylaminotetrazole. Methods of preparing the following compounds are found in the article. Preparation and Hydrogenation of Azomethines Derived From S-Aminotetrazole, by Ronald A. Henry and William G. Finnegan, published in The Journal of the American Chemical Society, 76, 926 (1954) 5- heptylaminotetrazole, 5-octylaminotetrazole and S-decylaminotetrazole. The preparation of 1-(m-chlorophenyl)- S-aminotetrazole is given in the article Thermal Isomerization of Substituted S-Aminotetrazoles, by Ronald A. Henry, William G. Finnegan, and Eugene Lieber, published in The Journal of the American Chemical Society, 76, 88 (1954). The method of preparing the following compounds is given in the article, Mono-Alkylation of Sodium S-Aminotetrazole in Aqueous Medium, by Ronald A. Henry and William G. Finnegan, published in The Journal of the American Chemical Society, 76, 923 (1954): 2-methyl-5-aminotetrazole, 2-ethyl-5-aminotetrazole, 2-methyl-5-methylaminotetrazole and 2-methyl-5- nitrotetrazole. The methods for preparing tetrazole, 5- dimethyltetrazole, 5-diallylaminotetrazole and Z-ethyltetrazole are Well known in the art. The following are new compounds for which the methods of preparation are given below: 1-butyl-5-butylaminotetrazole, 1-allyl-5-allyl aminotetrazole, ethyl (1-tetrazolyl)acetate, ethyl (2-tetrazlyl)acetate, B-(1-tetrazolyl)ethyl acetate, fi-(2-tetrazolyl)ethyl acetate, ethyl (l-methyl-S-tetrazolyl)acetate, ethyl (2-methyl-5-tetrazolyl)acetate, 1,4-bis (l-methyl-S- tetrazolyl)butane, 1,4-bis (2-methyl-5-tetrazolyl)butane,

I -Buty l -5-Butylaminotezrazole The compound was made in a similar fashion from 1,3- dibutylthiourea with a yield of 86%. Two recrystallizations from ethyl acetate-petroleum ether (1:10) gave a product melting between 74-76 C.

Analysis Carbon Hydrogen Nitrogen Calculated (CgI-I 9N5) 54. 79 9. 71 35. 51 Found; 54.. 92-54. 86 9. 22-9. 23 35. 66

Ethyl (1- and 2-Tetraz0lyl)Acetates Tetrazole (41.9 g., 0.599 mole) was suspended in 100 g ml. of absolute ethanol in a one liter, three necked, round bottom flask, equipped with a mechanical stirrer, additional funnel, and a reflux condensed. The tetrazole was neutralized to the phe-nophthalein end point by the addition of a solution of 39.6 g. (0.599 mole) of 85% potasflask and the solution was heated to reflux.

I-(S-tetrazolyl)-2-nitroguanidine and the guanidinium salt of 1-( S-tetrazolyl -2-nitroguanidine.

J -A llyl-5-A llylaminotetrazole The compound Was prepared in 82% yield from 1,3-di- Analysis Carbon Hydrogen Nitrogen Calculated (C1H N 51. 44 6. 69 41. 89 Found 51.08 6. 31 42. 63

sium hydroxide in 100 ml. of ethanol, and the solution was heated to boiling on a steam bath. Ethyl bromoacetate g., 0.599 mole) was then added as rapidly as the reflux permitted and the resulting homogeneous solution was heated and stirred for two hours. Potassium bromide precipitated as thereaction proceeded. The reaction mixture was then cooled to room temperature, the potassium bromide removed by filtration and the filtrate evaporated to dryness in vacuo on a steam bath. The residue was extracted with three 100' ml. portions of methylene chloride. The methylene chloride solution was dried over magnesium sulfate and evaporated to' dryness, leaving 86.2 g. (92.2% yield) of impure ethyl tetrazolylacetates as a viscous oil. Distillation at 1 mm. pressure yielded 23.2 g. (24.8% yield) of ethyl (2-tetrazolyl)- acetate, B.P. 83.5-84 C., M.P. 51-52" C.

The residue of ethyl l-tetrazolyDacetate (42.1 g., yield 45%) was distilled in a Hickman still at 10- mm. pressure and 90-100 C. pot temperature.

Analysis Carbon Hydrogen Nitrogen Calculated (CgIIsOzNJ) 38. 46 5.16 35. 89 Found 38. 99 4. 69 35. 06

B-(J- and 2Tetraz0lyl)Ethyl Acetates The compounds were prepared from land 2-(2-hydroxyethyl)tetrazoles which were prepared as follows: A suspension of 70 g. (1.0 mole) of recrystallized tetrazole in ml. of water in a two liter round bottom flask was neutralized to the phenolphthalein end point with a solution of 4125 g. (1.0 mole) of 97% sodium hydroxide in 150 ml. of water. A reflux condenser was attached to the 2-chloroethanol (101 g., 1.25 moles) was then added through the condenser as rapidly as the rate of reflux permitted. After the solution had been refluxed overnight, the Water was removed by vacuum evaporation ona steam bath. The hydroxyethyltetrazoles in the residue were separated from the sodium chloride by extraction with one 300 ml. and three 100' ml. portions, of boiling acetone. The acetone solution Was vacuum evaporated to leave 113.3 g. (99.34%) of mixed hydroxyethyltetrazoles. This mixture was dehydrated by azeotropic distillation with benzene and the excess benzene removed by vacuum evaporation. Acetylation of the hydroxyethyltetrazoles was accomplished by heating the mixture with a large excess of acetic anhydride for 2 hours on a steam bath. The excess anhydride and the acetic acid produced were removed by vacuum distillation. Fractionations of the residue Analysis Carbon Hydrogen Nitrogen B(2-tetrazolyl) ethyl acetate:

Calculated (CsHsOzNl) 38. 46 5.16 35.89 Found 37. 74 3. 93 87. 71 fi-(l-tetrazolyl) ethyl acetate Calculated (C5HsOzN4) 38. -16 5.16 35. 89 Found 40. 46 3. 29 38. 21

Ethyl (1- and Z-Methyl-S-Tetrazolyl) Acetates Analysis Carbon Hydrogen Nitrogen Calculated (C5HEO2N4) 38. 46 5.16 35.89 Found 38. 30 4. 46 35- 83 For the preparation of ethyl (1- and 2-methyl-5- tetrazolyl)-acetates, ethyl-(S-tetrazolyl) acetate (62.4 g., 0.4 mole) in 200 ml. of 95% ethanol was neutralized to a phenolphthalein end point with a 50 percent solution of sodium hydroxide. The solution contained in the two liter round bottom flask equipped with a condenser was then heated to reflux and 62.5 g. (0.44 mole) of methyl iodide was added through the condenser as fast as the rate of reflux permitted. After a total of 17 hours reflux, the solution was stripped to dryness in vacuo on a steam bath and the residue extracted with three 100 ml. portions of methylene chloride. The methylene chloride solution was dried over magnesium sulfate, filtered and evaporated. The residue from the methylene chloride solution was dissolved in 200 ml. of isopropanol. Chilling this solution yielded 20.53 g. (30.2%) of ethyl (l-rnethyl-S-tetrazolyl) acetate having a melting point of 6768 C.

Analysis Carbon Hydrogen Nitrogen Calculated otumotNi) 42. 35 5. 92 32. 93 Found 41. 5. 80 32. 77

The isopropanol filtrate was evaporated to dryness and the residue was distilled, yielding 28.95 g. (42.6% yield) of ethyl (Z-rnethyl-S-tetrazolyl) acetate having a boiling point of 103-l04 C. at 0.8 mm. pressure.

Analysis Carbon Hydrogen Nitrogen Calculated (C5H10N4) 42. 35 5. 92 32. 93 Found 41. 79 5.35 33. 27

Recrystallization of the distillation residue yielded an additional 7.13 g. (IO-5%) of ethyl (1methyl-5-tetrazolyl) acetate.

1,4-Bis (1- and Z-methyl-S-Tetrazolyl)Butanes Herbert (Journal of Organic Chemistry, vol. 15, 1082 (1950)). The product was isolated by dissolving the reaction mixture in ml. of ice water and acidifying the solution with 20 ml. of concentrated hydrochloric acid. The precipitated 1,4-bis (5-tetrazolyl)butane was removed by filtration, washed on the filter'with three, 50 ml. portions of ice water and air dried to give 16.18 g. of product. Recrystallization from water yielded 14.04 g. of pure product having a melting point of 204205 C.

Analysis Carbon Hydrogen Nitrogen Calculated (C H Na) 37. 10 5. 19 56. 71 Found 37. 15 4. 83 68. 12

For the preparation of the 1,4-bis (1- and Z-methyl-S- tetrazolyl)butanes, 1,4-bis (5-tetrazolyl)butane (12.19 g., 0.063 mole) was suspended in 50 ml. of water, neutralized to a phenophthalein end-point with 50% sodium hydroxide solution and the solution diluted to a total volume of 100 ml. After the solution was warmed to 70 C., 17.5 g. (0.1386 mole) of dimethyl sulfate was added dropwise with stirring; 50% sodium hydroxide was added as necessary to maintain the phenolphthalein endpoint. The addition of dimethyl sulfate was complete in 30 minutes and the solution was stirred at 70 C. for an additional two hours. The solution was then concentrated in vacuo on a steam bath to about 25 ml. and extracted with three 50 ml. portions of ethylene chloride. The ethylene chloride solution was evaporated to dryness leaving 10.18 g. (72.8%) of methylated products as a semi-solid residue. This residue was slurried with 100 ml. of cold acetone and 2.03 g. (14.5%) of solid having a melting point of 139 This material was probably 1,4-bis (l-rnethyl-S-tetrazolyl)butane. The acetone filtrate was evaporated to dryness, leaving 7.98 g. (52.0%) of soft solid which was probably a mixture of 1,4-bis (2-methyl-5-tetrazolyl)- butane and 1-(l-methyl-S-tetrazolyl)-4-(2-methyl-5-tetra zolyl) butane.

Analysis: Nitrogen Calculated (C H14Ng) Found 51.6l51.135l.5

The basic solution remaining after extraction of the methylated bis tetrazolyl butanes was acidified with concentrated hydrochloric acid and extracted with ethylene chloride. Evaporation of the ethylene chloride left 2.92 g. of partially methylated products and starting material.

1-(S-Tetrazolyl)*-Z-Nizr0guanidine A solution of 6.1 g. (0.072 mole) of anhydrous S-aminotetrazole in ml. of water was adjusted to the phenolphthalein endpoint with a 50% solution of sodium hydroxide. S-methyl-N-nitroisothiourea (9.6 g., 0.072 mole) was then added and the resulting solution was heated un der reflux on a steam bath for 12 hours. The evolution of methyl mercaptan began immediately and was essen tially complete at the end of the heating period. The solution was cooled, filtered from a small amount of insoluble material, adjusted to pH 2 with concentrated hydrochloric acid, and cooled overnight at 5 C. The product was removed by filtration, washed with two small volumes of cold water, and air dried. The yield was 6.35 g. (51.6%). From the aqueous mother liquors 1.5 g. (anhydrous) of unreacted S-aminotetrazole was recovered. (In a second experiment the yield was 37.8%.) The crude product was recrystallized once from water (about 10 ml./g.) to give a fine white-granular powder which did not melt below 250 C. when heated slowly, but which decomposed vigorously at 240245 C. when plunged into a hot bath at this temperature.

Guanidinizim Salt of J-(S-Tctmzolyl)-2-Nitrogzmnidirze A slurry of, 17.0 g. of anhydrous S-aminotetra-zole in 80 ml. of cold water was treated with 18.0 g. of guanidinium carbonate at such a rate that the evolution of carbon dioxide was not excessive. When complete solution of these reactants was attained, 120 ml. of 95% ethanol and 29.4 g. of l-methyl-1-nitroso-2-nitroguanidine were added. A slow evolution of gas began immediately; after one week at room temperature the orange-yellow methylnitrosoni-troguanidine had disappeared completely and had been replaced by a white granular solid. The mixture was heated to dissolve the solid phase, then cooled overnight at 5 C. The solid was removed by filtration, washed with a small volume of cold water, and air dried. The yield was 10.3 g. A second crop of 5.0 g. was obtained by evaporating the filtrate under reduced pressure to 100 ml. and recooling to 5 C. The total recovery of guanidinium salt, melting point 236-240 C., amounted to 33.1% of theory. The impure salt can be recrystallized from either water mL/g.) or from 60% ethanol mL/ g.) and is recovered as white, rather :fiuffy rosettes which decompose at 240242 C. when plunged into a hot bath.

Analysis Carbon Hydrogen Nitrogen Calculated (CaIIeNuOz) 15. 58 3. 92 as. 65 Found 15. 55-15. 73 4.03-4.24 67.1-64.5

gun propellants is well demonstrated by the burning rate curves, Examples 26 and 27, respectively, of these two compounds presented in FIG. 4, the increase in burning rate being largely due to the presence of these compounds. Stability tests demonstrated that they have acceptable surveillance characteristics. In general, the use of I-(S-tetrazolyl)-2-nitroguanidine produces a two to threefold increase in the burning rate over that shown by comparable formulations with nitroguanidine, as shown in FIG. 4. The guanidiniurn salt of this compound in propellant compositions is seen to increase the burning rate appreciably over comparable formulations containing nitroguanidine.

A distinct advantage of the invention, resulting from the fact that the plasticizing agents contain a large percentage of nitrogen, is the fact that the agents contribute a smaller negative heat of explosion to the formulations, thus resulting in a more eliicient propellant in that more nitrocellulose and less nitroglycerin can be used. For example, the conventional plasticizers, diethylphthalate and ethyl centralite have heats of explosion of 1761 and 2412, respectively, while the heats of explosion of 1-ethyl-5-ethylaminotetrazole, ethyl (1-tetrazolyl)acetate and 1,5-dimethyl tetrazole are 1225, 693 and 970.7 cal/gram, respectively.

A further advantage of the invention over the prior art is the fact that it provides homogeneous, single phase, cool propellent compositions.

From the above description it is seen that the invention provides novel and effective propellent compositions, characterized by the addition thereto of tetrazole den'vatives, these derivatives serving not only as eifective plasticizers for the preparation of homogeneous compoi2 sitions but also increasing the burning rate of the compositions without detracting from their surveillance and other requisite characteristics.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Gas producing compositions consisting essentially of a first component about 45 to about of a material selected from the class consisting of nitrocellulose-nitroglycerin systems in which the components are present in weight percents of about 30-60 and 2545, respectively; nitrocellulose nitroglycerin-nitroguanidine systems in which the components are present in weight percents of about 19-30, 7-19 and 5157.5, respectively; nitrocellulose-nitroglycerin l (5 -tetrazoly1)-2-nitroguanidine systems in which the components are present in weight per-cents of about 30, 7 and 55, respectively; and nitrocellulose-nitroglycerin-guanidinium salt of 1-(5- tetrazolyl)-2-nitroguanidine systems in which the components are present in weight percents of about 30, 7 and 55, respectively, and as a second component from about 5 to about 50 weight percent of a material selected from the class consisting of N Rte-I l I l wherein R is hydrogen, lower alkyl, lower alkylene, nitro, lower aminoalkyl, lower aminoalkylene, aminophenyl, lower carboalkoxyalkyl, and lower acyloxyalkyl; and R and R are hydrogen, lower alkyl, lower alkylene, phenyl, lower carboalkoxy-alkyl and lower acyloxy alkyl, with the limitation that'R and R are not hydro gen when R is hydrogen.

2. The gas producing composition of claim 1 in which said second component is 1-ethyl-S-ethylaminotetrazole.

3. The gas producing composition of claim 1 in which said second component is 1,5-dimethyltetrazole.

4. The gas producing composition of claim 1 in which said second component is 2 methyl-S-methylaminotetrazole.

5. The gas producing composition of claim 1 in which said second component is 2-methyl-S-nitrotetrazole.

6. The gas producing composition of claim 1 in which Said second component is ethyl (l-tetrazOlyDacetate.

7. The gas producing composition of claim 1 in which said first component is a nitrocellulose-hitroglycerin-nitroguanidine system and said second component is 1- ethyl-S-ethylaminotetrazole.

8. The gas producing composition of claim 1 in which said first component is a nitrocellulose-nitroglycerin system and said second component is l-ethyl-S-ethylaminotetrazole.

9. The gas producing composition of claim 8 in which said second component is 1,5-dimethyltetrazole.

10. The gas producing composition of claim 8 in which said second component is 2-methyl-5-methylaminotetrazole.

11. The gas producing composition of claim 8 in which said second component is ethyl (l-tetrazOlyDacetate.

2,480,852 Hale et al. Sept. 6, 1949 

1. GAS PRODUCING COMPOSITION CONSISTING ESSENTIALLY OF A FIRST COMPONENT ABOUT 45 TO ABOUT 90% OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OF NITROCELLULOSE-NITROGLYCERIN SYSTEMS IN WHICH THE COMPONENTS ARE PRESENT IN WEIGHT PERCENTS OF ABOUT 30-60 AND 25-45, RESPECTIVELY; NITROCELLULOSE-NITROGLYCERIN-NITROGUANIDINE SYSTEMS IN WHICH THE COMPONENTS ARE PRESENT IN WEIGHT PERCENTS OF ABOUT 19-30, 7-19 AND 51-57.5, RESPECTIVELY; NITROCELLULOSE-NITROGLYCERIN-1-(5-TETRAZOLYL)-2-NITROGUANIDINE SYSTEMS IN WHICH THE COMPONENTS ARE PRESENT IN WEIGHT PERCENTS OF ABOUT 30, 7 AND 55, RESPECTIVELY; AND NITROCELLULOSE-NITROGLYCERIN-GUANIDINIUM SALT OF 1-(5TETRAZOLYL)-2-NITROGUANIDINE SYSTEMS IN WHICH THE COMPONENTS ARE PRESENT IN WEIGHT PERCENT OF ABOUT 30,7 AND 55, RESPECTIVELY, AND AS A SECOND COMPONENT FROM ABOUT 5 TO ABOUT 50 WEIGHT PERCENT OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OF 